The present disclosure relates to a magnetostrictive torque sensor and a torque detection method.
There exists a magnetostrictive torque sensor that detects a torque of a rotating shaft or a stationary shaft by using a magnetostriction inverse effect that occurs on surfaces of the shafts. The magnetostriction inverse effect is a magnetic deformation phenomenon in which a deformation occurs on shaft surfaces in a tension direction (a plus 45-degree-angle direction, for example) and a compression direction (a minus 45-degree-angle direction, for example) when a torque affects a rotating shaft or a stationary shaft, with a resultant magnetic permeability increasing in the tension direction and decreasing in the compression direction. The magnetostrictive torque sensor includes a first detection coil that is disposed for detecting a magnetic permeability change in a first direction (the plus 45-degree-angle direction, for example) on the shaft surface; and a second detection coil disposed for detecting a magnetic permeability change in a second direction (the minus 45-degree-angle direction, for example) on the shaft surface.
There exist various types of magnetic torque sensors according to different detection coils. There are proposed various methods using a pair of U-shaped cores around which detection coils are wound (see Japanese Published Unexamined Patent Application No. JP-A-2001-133337, for example), a pair of detection coils that are formed to be a figure eight (see Japanese Published Unexamined Patent Application No. JP-A-6-221940, for example), a pair of detection coils that are formed to be a wave shape (see Japanese Published Unexamined Patent Application No. JP-A-6-273247, for example), and a pair of detection coils that are formed to be a hollow tube shape. In addition, the method using the hollow-tubular-shaped detection coils includes magnetic anisotropic portions that are formed to be a slit, groove, thin film, etc. on a shaft surface; and no magnetic anisotropic portion on a shaft surface (see Japanese Published Unexamined Patent Application Nos. JP-A-7-83769, JP-A-11-37863 and JP-A-2005-208008, for example).